Air quality is assessed by measuring levels of gases and particles in the surrounding (ambient) air. The United States Environmental Protection Agency (EPA) examines these levels using monitoring stations scattered throughout the United States. In Larimer County, the EPA measures three major pollutants: ozone, carbon monoxide, and particulates. Monitors for all three of these pollutants are located in Fort Collins; there are also two ozone monitors located in Rocky Mountain National Park.

The EPA has set specific standards for these pollutants. Areas with pollutant levels that exceed the prescribed standards are subject to action by the EPA. For an explanation of the EPA's methodology, see Industry Standards or Targets.

Typically, light, easterly winds pick up VOC and NOx pollutants and intense summer sunlight 'bakes' the pollutants, resulting in higher concentrations along the foothills. High ground-level ozone concentrations are known to cause health problems, especially in vulnerable populations, and can also cause serious damage to plants and trees.

On November 20, 2007, the EPA designated the Denver/North Front Range region (including Larimer County) as nonattainment for the 8-hour ozone standard of 0.080 parts per million (ppm) adopted in 1997. The 2008 Ozone Action Plan contains a map of the nonattainment area on page 16.

Beginning in November 2010, vehicles registered in Larimer County have been required to undergo a complex emissions test measuring carbon monoxide, hydrocarbons, and nitrogen oxides.

What this chart shows:

What the above data tell us:

In 2012, carbon monoxide levels at the Mason Street monitoring site were 350% below the national standard, showing a significant improvement in air quality. Yearly measurements reflect the national trend of decreasing carbon monoxide concentrations due to new car regulations.

The EPA standard is met when the daily maximum 8-hour average reading does not exceed 9 ppm.

What the above data tell us:

Until 1999, Fort Collins only monitored PM10 particulates (i.e. particulate less than 10 micrometers in size) from a monitor located at the Larimer County Courthouse (200 W. Oak). In 1999, a second monitoring station was added at 251 Edison Drive. The Edison Drive monitoring station measured PM10 and PM2.5 particulates (particulate less than 2.5 micrometers in size).

In December 2006, the Environmental Protection Agency (EPA) revised the 1997 standards from 65 micrograms per cubic meter (µg/m3) to 35 µg/m3. Even with this reduction, Fort Collins remains well below the EPA's standard of 35 µg/m3. When the EPA revised the 1997 standards, it also revoked the PM10 annual standard due to a lack of evidence linking health problems to long-term exposure to coarse particle pollution. Currently, the Edison station is the only PM2.5 monitoring station in Larimer County.

PM2.5 levels in Fort Collins are generally much lower than the EPA regulatory limits and efforts such as improved street sweeping and sanding, and regulations restricting wood burning, help keep particulate levels low. Common sources of particulate include dust, wood burning, smoke stacks, natural fires, and gasoline/diesel combustion.

The EPA standard is met when the 3-year average of the 98th percentile of 24-hour concentrations at each site within an area does not exceed 35 µg/m3.

Additional Information:

Sources and Effects of Three Major Pollutants

Ozone (O3): Emitted primarily by motor vehicles. Ozone is a major component of photochemical smog. Ozone has been linked to health concerns such as respiratory irritation, chronic bronchitis, and decreased lung function. Those with existent respiratory complaints, children, and the elderly are most affected by high ozone concentrations.

The Fort Collins ozone monitors are located at 708 S. Mason and 3416 La Porte Avenue near Horsetooth Reservoir. A special monitor was installed at 11822 Rist Canyon Road in 2009 and will likely be removed due to redundancy. The Rocky Mountain National Park monitor is located near the Longs Peak Ranger Station.

Carbon monoxide (CO): Emitted primarily by motor vehicles. When CO enters the bloodstream, it reduces the delivery of oxygen to the body's organs and tissues. Health threats are most serious for those who suffer from cardiovascular disease, particularly those with angina or peripheral vascular disease.

The Fort Collins carbon monoxide monitors are located at 708 S. Mason and 4407 S. College.

Industry Standards or Targets:

The original national standard for O3 concentration (ozone) was 0.12 ppm, using the second-highest yearly mean of readings taken over a 1-hour period. However ozone levels can fluctuate throughout the day at any given location. In 1997, the EPA established a revised standard of 0.080 ppm averaged over an 8-hour period. Attainment of the standard is based on the 4th maximum 8-hour ozone concentration recorded at each monitoring location each year, averaged over a three-year period.

On March 12, 2008, the EPA revised the standard [pdf] again to a level of 0.075 parts per million (ppm), and according to the Colorado Department of Public Health and Environment, the region has until 2020 to reach that standard. Attainment is based on the 3-year average of the annual fourth-highest daily maximum 8-hour average at every monitor within the region. The revised standard attempts to account for daily fluctuations in ozone, resulting in a more accurate picture of actual ozone levels. For detailed information concerning the revised ozone standard, please visit the EPA's webpage, National Ambient Air Quality Standards (NAAQS).

The national standard for CO concentration (carbon monoxide) is 9 ppm (parts per million), not to be exceeded more than once per year over an 8-hour period.

From 1997 through 2006, the national standard for PM2.5 (particulates) was 65 µg/m3. Effective December 17, 2006, the EPA revised the standard for PM2.5 to 35 µg/m3, calculated by the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor.